Oxidation catalyst and oxidation process using the same

ABSTRACT

In the presence of (1) an oxidation catalyst comprising a crystalline complex of manganese with an N,N&#39;-disalicylidenediamine (e.g., N,N&#39;-disalicylidene C2-8 alkylenediamines and N,N&#39;-disalicylidene C6-12 arylenediamines), or (2) an oxidation catalyst comprising the above complex and a basic nitrogen-containing compound, a substrate (e.g., beta-isophorone or a derivative thereof) is oxidized with molecular oxygen to produce a corresponding oxide (e.g., ketoisophorone). Ketoisophorone can be obtained from beta-isophorone with high conversion and high selectivity.

FIELD OF THE INVENTION

The present invention relates to an oxidation catalyst, an oxidationprocess using the same, and a process for producing ketoisophorone fromβ-isophorone.

BACKGROUND OF THE INVENTION

Ketoisophorone (4-oxoisophorone), a useful intermediate for a startingmaterial of medicines, perfumes, condiments, and for polymer, isproduced from isophorone and the like. For example, as a process forproducing 4-oxoisophorone by oxidizing α-isophorone with oxygen, therehave been proposed a method in which α-isophorone is oxidized withoxygen in the presence of a phosphomolybdic acid or a silicomolybdicacid [Japanese Patent Publication No. 30696/1980 (JP-B-55-30696)], amethod in which a-isophorone is oxidized with oxygen in the coexistenceof a phosphomolybdic acid or a silicomolybdic acid and an alkaline metalcompound or an aromatic amine [Japanese PatentApplicationLaid-OpenNo.191645/1986 (JP-A-61-191645)], and a method inwhich a-isophorone is oxidized with oxygen in the presence of a vanadiumcatalyst [Japanese Patent Application Laid-Open No. 93947/1975(JP-A-50-93947)]. Japanese Patent Application Laid-Open No. 81347/1974(JP-A-49-81347) discloses a method for producing 4-oxoisophorone byoxidizing a-isophorone with an alkaline metal chromic acid salt or adichromate or a chromium trioxide. In the Chem. Lett. (1983), (7), 1081,there is disclosed a method for producing 4-oxoisophorone by oxidizinga-isophorone using t-butylhydroperoxide in the presence of a palladiumcatalyst. However, in these methods, the selectivity of ketoisophoroneis reduced, therefore separation of the formed by-product(s) or a metalcatalyst and purification of the object compound are complicated.Moreover, these methods involve using a heavy metal compound requiringspecial treatment, such as chromium, or a peroxide needed to be handledwith care, which results in a decrease in working efficiency.

Moreover, as a method for producing ketoisophorone from β-isophorone,Japanese Patent Application Laid-Open No. 125316 (JP-A-51-125316)discloses a method for producing an ethylenically unsaturateddicarboxylic acid by oxidizing β-ethylenically unsaturated ketone withmolecular oxygen or a molecular oxygen-containing gas in the presence ofan inorganic base or an organic base and a cobalt or manganese chelate.In this method, however, the yield of ketoisophorone is low due to theuse of a straight-chain secondary or tertiary amine such astriethylamine as the organic base.

In Japanese Patent Application Laid-Open No. 53553/1998 (JP-A-10-53553)discloses a method for producing ketoisophorone by oxidizingβ-isophorone with molecular oxygen in the presence ofbis(2-hydroxybenzylidene)ethylenediamine-manganese complex salt (i.e.,manganese-salene), an organic base, a specific substance having acatalytic action (e.g., acetylacetone), and water. In the literature,there is recited as the manganese complex salt a complex in which 1 moleof bis(2-hydroxybenzylidene)ethylenediamine is coordinated relative to 1mole of manganese. However, even in the above method using the abovemanganese complex salt, the conversion and the selectivity of asubstrate are not improved enough. Particularly, a higher concentrationof β-isophorone in the reaction system causes a considerable decrease inthe yield of ketoisophorone. For example, when the concentration ofβ-isophorone is 20% by weight or more, the conversion and/or theselectivity is decreased to a large extent. Therefore, relatively largeamounts of a manganese complex salt and an organic base are required foran improved conversion. Further, a lower concentration of oxygenremarkably decreases the reaction rate.

SUMMARY OF THE INVENTION

Thus, an object of the present invention is to provide an oxidationcatalyst capable of oxidizing a substrate with high conversion and highselectivity regardless of the concentration of the substrate, and anoxidation process using the same.

Another object of the present invention is to provide an oxidationcatalyst capable of oxidizing a substrate with high conversion and highselectivity even used in a catalytic amount, and an oxidation processusing the same.

Further object of the present invention is to provide an oxidationcatalyst which ensures the efficient proceeding of an oxidative reactionefficiently proceeds even with, as a source of molecular oxygen, a lowoxygen content gas, such as air, and an oxidation process using thesame.

Still further object of the present invention is to provide an oxidationcatalyst capable of producing ketoisophorone with maintaining highconversion and high selectivity even with a high β-isophoroneconcentration and a low oxygen concentration, and a process forproducing ketoisophorone using the same.

The inventors of the present invention did intensive investigations toachieve the above objects and found that, even in a reaction system witha high substrate (e.g., β-isophorone) concentration and a low oxygenconcentration, the substrate can be oxidized with high conversion andhigh selectivity by using a specific complex comprising manganese and anN,N′-disalicylidenediamine, and that the conversion and the selectivityare remarkably improved by further employing or incorporating a basicnitrogen-containing compound in combination with the above complex. Thepresent invention was accomplished based on the above findings.

Accordingly, the oxidation catalyst of the present invention comprise(1) a crystalline complex of manganese with anN,N′-disalicylidenediamine, or (2) the above complex (1) and a basicnitrogen-containing compound. The melting point of the above crystallinecomplex may be about 190 to 240° C.

The present invention further includes an oxidation process in which asubstrate is oxidized with oxygen in the presence of the above oxidationcatalyst, for example, a process which comprises oxidizing β-isophoroneor a derivative thereof with molecular oxygen to produce a correspondingketoisophorone or a derivative thereof.

In the specification, the term “N,N′-salicylidenediamine” is taken tomean that an N,N′-salicylidenediamine may have a structure in which asalicylidene group is bound to a nitrogen atom of each amino group of analiphatic, alicyclic, or aromatic diamine.

DETAILED DESCRIPTION OF THE INVENTION

[Complex]

A complex of the oxidation catalyst of the present invention iscrystalline and comprising manganese and an N,N′-disalicylidenediamine.The valence of manganese is usually in the range of divalent totetravalent (particularly, divalent). In addition to manganese, thecomplex may further comprise other transition metal component, ifneeded, for example, a transition metal element of the Groups 3 to 12 ofthe Periodic Table of the Elements [e.g., the group 5 elements (e.g., V,Nb), the group 6 elements (e.g., Cr), the group 7 elements (e.g., Re),the group 8 elements (e.g., Fe, Ru), the group 9 elements (e.g., Co,Rh), the group 10 elements (e.g., Ni, Pd), and the group 11 elements(e.g., Cu)].

The above N,N′-disalicylidenediamine has a structure in which asalicylidene group is bound to each nitrogen atom of the two aminogroups of an aliphatic, alicyclic, or aromatic diamine. The manganesecomplex of the present invention comprising manganese and anN,N′-disalicylidenediamine ligand is represented by the followingfurmula:

wherein R¹, R², and R³ are the same or different and each represents analkylene group, a cycloalkylene group, or an arylene group and may havea substituent; R⁴ to R⁹ are the same or different and each representshydrogen atom, a halogen atom, an alkyl group, a hydroxyl group, ahydroxymethyl group, or an alkoxy group; the rings Z are aromatic rings;M stands for manganese; and n is 0 or an integer of not less than 1.

As a diamine corresponding to the above R¹, R², and R³ there may beexemplified aliphatic diamines such as a straight- or branched chainC₂₋₁₀ alkylenediamines and a C₂₋₁₀ alkylenediamine containing an iminogroup (NH group); alicyclic diamines such as a diaminocyclohexane; andC₆₋₁₂ aromatic diamines such as a diaminobenzene, a diaminonaphthalene,a biphenyldiamine and derivatives thereof.

Examples of the N,N′-disalicylidenediamine are N,N′-disalicylidene C₂₋₈alkylenediamines such as N,N′-disalicylidene ethylenediamine,N,N′-disalicylidene trimethylenediamine, andN,N′-disalicylidene-4-aza-1,7-heptanediamine (preferably,N,N′-disalicylidene C₂₋₅ alkylenediamine); and N,N′-disalicylidene C₆₋₁₂arylenediamines such as N,N′-disalicylidene-o-phenylenediamine, andN,N′-disalicylidene-2,2′-biphenylenediamine. Examples of theparticularly preferred N,N′-disalicylidenediamine areN,N′-disalicylidene C₂₋₄ alkylenediamines such as N,N′-disalicylideneethylenediamine and N,N′-disalicylidene trimethylenediamine.

As the aromatic rings Z, there may be exemplified hydrocarbon rings(e.g., benzene, naphthalene) and heterocycles (e.g., nitrogenatom-containing heterocycles such as pyridine, pyrazine, pyrimidine, andquinoline; sulfur atom-containing heterocycles such as thiophene; andoxygen atom-containing heterocycles such as furan). As to thesubstituents R⁴ and R⁹ of the aromatic rings Z, examples of the halogenatom are bromine, chlorine, and fluorine, and examples of the alkylgroup are C₁₋₆ alkyl groups such as methyl, ethyl, propyl, butyl, andt-butyl group. Examples of the alkoxy group are C₁₋₆ alkoxy groups suchas methoxy, ethoxy, propoxy, and butoxy groups. The substituents R⁴ andR⁹ are usually hydrogen atoms, C₁₋₄ alkyl groups, or hydroxymethylgroups.

In the complex shown by the above formula, n is 0 or an integer of notless than I (e.g., 1 to 5, particularly 1 or 2).

In the above complex, m+l mole of the N,N′-disalicylidenediamine iscoordinated to m mole of manganese (m is an integer of not less than 1),and thus the complex is structurally different from a conventionalmanganese complex in which 1 mole of the N,N′-disalicylidenediamine iscoordinated to 1 mole of manganese. Moreover, in contrast to theconventional manganese complex being noncrystalline (amorphous), thecomplex of the present invention is crystalline and shows a clearmelting point in accordance with a thermal analysis by TC/TDA. Themelting point of the complex is usually about 190 to 240° C. andparticularly about 200 to 220° C. Moreover, the complex of the presentinvention can be distinguished from conventional manganese complexes bywhether there is an absorption peak for the hydroxyl group in theinfrared absorption spectrum or not.

An oxidation catalyst comprising such complex is useful for producing anoxide (e.g., ketoisophorone or derivatives thereof) by oxidizing asubstrate (e.g., β-isophorone or a derivative thereof) with molecularoxygen. Moreover, the oxidation catalyst may comprise the above complexand a basic nitrogen-containing compound.

[Production Process of Complex]

The above complex can be obtained by coordinating an excess amount of anN,N′-disalicylidenediamine with a manganese compound. As the manganesecompound, there may be exemplified organic acid salts (e.g., acetates),halides (e.g., manganese chloride), and inorganic acid salts. Theproportion of the N,N′-disalicylidenediamine relative to the manganesecompound is about 0.5 to 5, preferably about 0.9 to 3, and particularlyabout 1 to 2 (molar ratio). Even if the proportions are almost equimolarwith each other, a complex in which a substantially excess mole of anN,N′ -disalicylidenediamine is coordinated can be obtained by liberatingor separating a manganese compound though deteriorated in yield.

The reaction may be conducted in an inert solvent (e.g., an organicsolvent such as an alcohol). Practically, the reaction is carried out inan atmosphere of an inert gas and can be effected usually with stirringat a temperature within the range of 70° C. to a reflux temperature of asolvent. The complex can be obtained by recovering or collecting thereaction product and, if needed, purifying by a recrystallizationtechnique, and drying.

[Basic Nitrogen-containing Compound]

A combination of the above complex and the basic nitrogen-containingcompound gives an oxidation cataloyst having a higher activity andremarkably improves the conversion of the substrate (e.g., β-isophorone)and the selectivity of the object oxide (e.g., ketoisophorone).

The basic nitrogen-containing compound includes not only aliphaticamines but also cyclic bases (alicyclic or aromatic amines), and thecyclic bases may be heterocyclic amines. The amines may be primary,secondary, or tertiary, and a tertiary amine is usually employed.

Examples of the aliphatic amines are mono-, di-, or tri-C₁₋₆ alkylaminessuch as dimethylamine, diethylamine, dibutylamine, triethylamine, andtributylamine; alkanolamines such as ethanolamine, diethanolamine, andtriethanolamine; alkylenediamines such as ethylenediamine,diethylenetriamine and butanediamine or N-substituted compounds of thealkylenediamines.

As the cyclic bases, there may be mentioned, for example, alicyclic oraromatic bases having at least one nitrogen atom. The alicyclic basesinclude alicyclic hydrocarbons having an amino group or an N-substitutedamino group (alicyclic amines), and compounds in which at least onenitrogen atom constitutes a hetero atom of the ring (nitrogen-containingheterocyclic compounds). Examples of the alicyclic amines includecycloalkylamines or derivatives thereof (mono- or di-C₁₋₄alkylaminocycloalkanes such as dimethylaminocyclohexane). Thenitrogen-containing heterocyclic compounds includes,for example, 5- to10-membered mono- and heterocyclic compounds such as pyrrolidine or itsderivatives [N-substituted pyrrolidines (e.g., N-C₁₋₄ alkylpyrrolidinessuch as N-methylpyrrolidine), substituted pyrrolidines (e.g., 2- or3-methylpyrrolidine, 2- or 3-aminopyrrolidine), or the like]; piperidineor its derivatives [N-substituted piperidines (e.g., N-C₁₋₄alkylpiperidine such as N-methylpiperidine; piperylhydrazine),substituted piperidines (o-aminopiperidine, m-aminopiperidine, andp-aminopiperidine)]; alkylene imines or its derivatives [hexamethyleneimine, N-substituted hexamethylene imines (e.g., N-methylhexamethyleneimine)]; piperazine or its derivatives [N-C₁₋₄ alkylpiperazines such asN-methylpiperazine; N,N′ -di-C₁₋₄ alkylpiperazines such asN,N′-dimethylpiperazine; 2-methylpiperazine]; and poly- and heterocycliccompounds such as azabicyclo C₇₋₁₂ alkanes (e.g., quinuclidine,1,4-diazabicyclo[2.2.2]octane (DABCO), 1,5-diazabicyclo[3.2.1)]octane,1,5-diazabicyclo[3.3.0]octane, 1,4-diazabicyclo[4.2.0]octane,1,5-diazabicyclo[3.3.1]nonane, 1,5-diazabicyclo[5.3.0]decane),azatricyclo C₈₋₁₆ alkanes (e.g., 1,5-diazatricyclo[3.3.0.0^(2.6)]octane, hexamethylenetetramine), and derivatives thereof.

Among these alicyclic bases, those containing at least one(particularly, 2) (e.g., 2 to 6) nitrogen atom are preferable(particularly, the above alicyclic bases having a nitrogen atom as ahetero atom), and examples of such alicyclic bases are 6 to 8-memberedmono- and heterocylcic compounds (e.g., piperazine, N-substitutedpiperazines, amino group-substituted piperazines); azabicyclo C₇₋₁₀alkanes (e.g., quinuclidine, DABCO, or its derivatives); andhexamethylenetetramine.

The aromatic bases includes aromatic hydrocarbons having an amino groupor an N-substituted amino group or both (aromatic amines), and aromaticcompounds in which at least one nitrogen atom constitutes a hetero atomof a ring (aromatic heterocyclic compounds). Examples of the aromaticamines are aniline or derivatives thereof (e.g., N,N′-di-C₁₋₄alkylanilines); toluidine or derivatives thereof (e.g., N,N′-di-C₁₋₄alkyltoluidines); and anisidine or derivatives thereof (e.g.,N,N′-di-C₁₋₄ alkylanisidines). As the aromatic heterocyclic compound, anaromatic compound having at least two nitrogen atoms in which at leastone nitrogen atom constitutes a ring is preferable. An examples of sucharomatic heterocyclic compound is a compound having a substituentcontaining at least a nitrogen atom (e.g., amino group, N-substitutedamino group) on an aromatic heterocyclic compound having at least onenitrogen atom as a hetero atom (e.g., pyridine) [e.g., 2-, 3-, or4-aminopyridine, 2-, 3-, or 4-mono or dialkylaminopyridines (e.g.,di-C₁₋₄ alkylaminopyridines such as dimethylaminopyridine), 2-, 3-, or4-piperidinopyridine, and 4-pyrrolidinopyridine]; pyrazine or itsderivatives (e.g., 2-methylpyrazine); phthalazine, quinazoline,quinoxaline, or derivatives thereof; phenanthroline or its derivatives(e.g., 1,10-phenanthroline); and 2,2-bipyridyl or its derivatives.N,N-dialkylaminopyridines, pyrazine, phenanthroline, or derivativesthereof are particularly preferred.

In the above cyclic base, another nitrogen atom(s)than the oneconstituting a ring comprises preferably a tertiary amino group, and thenitrogen atom constituting the ring may have a substituent other than ahydrogen atom (e.g., a C₁₋₄ alkyl group). The basic nitrogen-containingcompound can be used either singly or as a combination of two or morespecies.

The proportion of the basic nitrogen-containing compound relative to theabove complex (the former/the latter) can suitably be selected from therange of about 0.1/1 to 500/1 (molar ratio) and preferably about 0.5/1to 250/1 (e.g., 0.8/1 to 250/1).

[Oxidation reaction]

By oxidizing a substrate with molecular oxygen using the oxidationcatalyst of the present invention, the corresponding oxide can beproduced in high yield even if the concentration of the substrate in areaction system is high. Moreover, its high activity permits aremarkable decrease in the amount of the oxidation catalyst as comparedto conventional manganese complexes, and therefore an oxide can beproduced with high conversion and high selectivity even in the presenceof an exceedingly minute amount of the oxidation catalyst. Further,since the oxide can be produced with high conversion and highselectivity even if the concentration of oxygen is low, air or the likecan also be used as an oxygen source.

[Amount of Catalyst]

The amount of the oxidation catalyst to be used is, for example, about0.001 to 5 parts by weight, preferably about 0.01 to 1 part by weight,and more preferably about 0.05 to 0.5 part by weight, relative to 100parts by weight of β-isophorone or a derivative thereof. The amount ofeach constituent of the oxidation catalytic system relative to 1 mole ofβ-isophorone or a derivative thereof is as follows.

Complex: about 1×10⁻⁵ to 1×10⁻² mole (preferably, about 1×10⁻² to 0.5mole)

Basic nitrogen-containing compound: about 5×10⁻² to 1 mole (preferably,about 1×10⁻² to 0.5 mole).

[Substrate]

The species of the above-mentioned substrate is not particularlylimited, and there may be exemplified β-isophorone(3,5,5-trimethylhex-3-ene-1-one) or derivatives thereof and compoundshaving a structure similar to that of β-isophorone, for example,compounds having a 3-cyclohexenone skeleton. Particularly, the oxidationcatalyst of the present invention is useful in producing thecorresponding ketoisophorone by oxidizing β-isophorone or a derivativethereof with molecular oxygen.

The concentration of the substrate in the reaction system is notparticularly restricted, and the object compound can be produced withhigh conversion and high selectivity even at aconcentrationof,e.g.,about5to50% by weight. Particularly, even if theconcentration of the substrate (e.g., β-isophorone or a derivativethereof) is 10 to 50% by weight and preferably 20 to 50% by weight, theoxidative reaction can be effected with retaining or maintaining aselectivity of 90% or higher (e.g., a selectivity of about 93 to 97%),and therefore, the oxidation and the catalyst of the present inventionhas great advantages and is remarkably useful in view of industry.

In the present invention, in addition to oxygen and oxygen-containinggases, a compound generating molecular oxygen is also employed as anoxygen source so far as capable of providing molecular oxygen. As theoxygen source, highly pure oxygen or a high oxygen content gas may beused, the oxygen gas diluted with an inert gas, e.g., nitrogen, helium,argon, or carbon dioxide is preferably supplied to the reaction system.Moreover, with the oxidation catalytic systems of the present invention,the substrate can be oxidized effectively even with air instead ofoxygen as the oxygen source. The use of air as the oxygen source is notonly highly advantageous in view of economics but also reduces thedanger of explosions encountered in industrialization.

The oxygen concentration of the oxygen source is, for example, about 5to 100% by volume, preferably about 5 to 50% by volume, and particularlyabout 7 to 30% by volume. Even at such a low oxygen concentration as ofabout 8 to 25% by volume, the oxidative reaction effectively proceeds.

When supplying molecular oxygen to a reaction vessel or container, thereaction may be carried out in a closed system with enough molecularoxygen previously supplied, or may be conducted in a continuous streamof molecular oxygen. In the case of a stream of molecular oxygen, theflow rate is, for example, about 0.1 to 10 L/min and preferably about0.5 to 5 L/min per unit volume (IL) of the vessel.

The oxidative reaction may be either gas-phase oxidation or liquid-phaseoxidation. The reaction may be conducted in the absence of a solvent,and usually carried out in an inert solvent.

As the reaction solvent, hydrophilic solvents or hydrophobic solventssuch as hydrocarbons, halogenated hydrocarbons, esters, ketones, ethersand aprotic polar solvents may be used provided that they do not impairthe oxidative reaction. Since water is produced in the oxidativereaction, some species of basic nitrogen-containing compound aredifficult to recover and sometimes the solvent can not be recycled. Insuch case, a water-insoluble (or hydrophobic) organic solvent ispreferable. Examples of the water-insoluble organic solvent arealiphatic hydrocarbons solvents such as hexane, heptane, and octane;aromatic hydrocarbon such as benzene, toluene, and xylene; alicyclichydrocarbons such as cyclohexane; ketones (particularly, dialkylketones) such as methyl ethyl ketone and dibutyl ketones (e.g.,diisobutyl ketone, di-t-butyl ketone); ethers such as diethyl ether,diisopropyl ether, dibutyl ether, tetrahydrofuran, dioxane, ethyleneglycol monomethyl ether, ethylene glycol dimethyl ether, diethyleneglycol monomethyl ether, and diethylene glycol dimethyl ether;halogen-containing solvents such as monochloroethane, dichloroethane,chloroform, carbon tetrachloride, and 1,2-dichloroethane; and esterssuch as methyl acetate, ethyl acetate, and butyl acetate. Dialkylketones are preferable and dibutyl ketones are particularly preferred.

The amount of the solvent to be used is not particularly restricted andmay be selected from within the range of about 5 to 70% by weight andpreferably about 15 to 60% by weight (e.g., 20 to 55% by weight).

The proportion of the water content in the reaction system can beselected from within the range not adversely affecting on the reactionsuch as inactivation of the catalytic system, and is about 1% by weightor less (about 0.001 to 1% by weight) and preferably about 0.5% byweight or less (about 0.001 to 0.5% by weight). Despite acceleration ofthe reaction at the initial stage, the water content exceeding 1% byweight results in a subsequent cessation of the reaction or a decreasein selectivity. The water in the reaction system includes not only thewater contained at the beginning or initial stage of the reaction butalso the water produced by the reaction. In the present reaction system,there is usually present a finite amount of water. It is desirable thatthe water produced by the reaction is removed from the system. Theamount of the produced water varies with the concentration ofβ-isophorone substrate, and the amount of the water to be removed is atleast about 30% by weight, preferably at least about 50% by weight, andmore preferably at least about 80% by weight, relative to the totalamount of the water produced.

The reaction temperature can be selected from within the range of, e.g.,about 10 to 100° C. (preferably about 20 to 60° C.) according to thereaction rate, selectivity, and the solvent to be used. The reaction canbe conducted either at atmospheric pressure or under applied pressure[to about 150 atm (152×10⁵ Pa)] and preferably at atmospheric pressure.The reaction time (or residence time) is not particularly restricted andcan be selected from within the range of about 10 seconds to 24 hours,depending upon the system of the reaction (e.g., a continuous system ora batch system).

The reaction can be carried out in a conventional system such as a batchsystem, a semi-batch system, or a continuous system. In the continuoussystem, portions of the catalyst are continuously or intermittentlyremoved from a reactor for regeneration, and the regenerated catalyst(i.e., a complex of a transition metal with anN,N′-disalicylidenediamine) may be recycled to the reactor to be reused.In the batch system, the catalyst or the constituents of the catalystmay be separated and recovered from a reaction product after completionof the reaction, wholly or partially regenerated and may be reusedrepeatedly as a catalyst for the reaction.

An oxide produced by the reaction (e.g., ketoisophorone) can easily beseparated and purified with a conventional separation technique such asfiltration, condensation, distillation, extraction, crystallization,recrystallization and column chromatography, or a combination thereof.Particularly, according to the present invention, the conversion ofβ-isophorone and the selectivity of ketoisophorone can be significantlyimproved, and the production of by-product(s) is remarkably inhibited.Therefore, even though the separation and purification step is requiredof ketoisophorone, ketoisophorone can be separated and purified witheasiness and efficiency, and therefore need not be highlyseparation-purified.

According to the present invention, the substrate can be oxidized withhigh conversion and high selectivity regardless of its concentration byusing the crystalline manganese complex of manganese with theN,N′-disalicylidenediamine. Moreover, even if the amount of the catalystis extremely minute, the substrate can be oxidized with high conversionand high selectivity. Further, even when the oxygen concentration of themolecular oxygen source is low as in the case of air, the oxidationcatalyst of the present invention proceeds efficiently an oxidativereaction. Therefore, when the catalyst of the present invention isapplied to the oxidation of β-isophorone, even if the concentration ofβ-isophorone is high and the oxygen concentration is low, ketoisophoronecan be produced with retaining high conversion and selectivity.Particularly, even in the reaction system with a high β-isophoroneconcentration, it is possible to maintain high selectivity and produceketoisophorone with an improved efficiency.

EXAMPLES

The following examples are intended to show the present invention infurther detail and should be no means be construed as defining the scopeof the invention.

The substrate, transition metal complex, nitrogen-containing compounds,and the solvent used in Examples and Comparative Examples are asfollows.

1. Substrate: β-isophorone (β-IP)

2. Manganese complex

(b-1): crystalline manganese complex

A reactor was fed with 169 g (630 mmol) of theN,N′-disalicylideneethylenediamin (EDSA) and 5,000 ml of methanol, andthe EDSA was dissolved at a reflux temperature under a nitrogen stream.According to the method recited in Inorg. Synth. 3 (1950) 196,N,N′-disalicylideneethylenediamine (EDSA) had been synthesized byrefluxing 2 mol of salicylaldehyde and 1 mol of ethylenediamine inethanol for 6 hours.

A solution of 156 g (637 mmol) of manganese acetate·tetrahydrate Mn(OAc)₂.4H₂O and 1,500 ml of methanol was added to the above-describedsolution of EDSA in methanol at 50° C. in a nitrogen stream, and themixture was reacted at a reflux temperature in a nitrogen stream for 8hours. After the completion of the reaction, the mixture was allowed tostand overnight in an atmosphere of nitrogen to be cooled, and stored ina container (or vessel) in which a nitrogen gas is flowing. With anitrogen gas flowing through the container, the mixture was filtered anddried in vacuo at 80° C. for 6 hours to obtain 135.4 g of crystals(yield: 70%).

Thermal analysis (TC/TDA) of the crystalline complex showed the meltingpoint of 207.8° C.

Elemental analysis Found C: 65.5, H: 5.2, N: 9.5 Calculated C: 65.2, H:5.1, N: 9.5 (corresponding to the above formula in which n = 0)Calculated C: 63.3, H: 4.9, N: 9.2 (corresponding to the above formulain which n = 0)

(b-2): Noncrystalline manganese complex

A manganese complex was obtained according to the method recited in theJ. Am. Chem. Soc., 108 (1986) 2317. In other words, to a mixed solutionof 2.15 g (8 mmol) of EDSA and 50 ml of methanol was added a solution of0.90 g (16 mmol) of potassium hydroxide and 20 ml of methanol.Thereafter, to the resultant mixture was added a solution of 1.98 g(8.08 mmol) of manganese acetate·tetrahydrate Mn (OAc)₂.4H₂O and 30 mlof methanol in a nitrogen stream, and the reaction mixture was refluxedat a ref lux temperature for 5 hours. Thereafter, the reaction mixturewas cooled to room temperatures taking 2 hours, and then filtered. Thecake or residue was washed with 10 ml of methanol, and filtered, anddried in vacuo at 100° C. for 8 hours to obtain a manganese complex.

Thermal analysis (TC/TDA) of the manganese complex showed no clearendoergic peak and revealed the complex to be noncrystalline(amorphous). The melting point of the sole EDSA was 127.6° C.

Elemental analysis Found C: 59.6, H: 4.3, N: 8.7 Calculated C: 59.8, H:4.4, N: 8.7

3. Nitrogen-containing compound

(c-1): 1,4-diazabicyclo[2.2.2]octane (DABCO)

(c-2): 4-dimethylaminopyridine

(c-3): 2-dimethylaminopyridine

(c-4): 1,10-phenanthroline

(c-5): triethylamine

4. Solvent: diisobutyl ketone

Examples 1 to 8 and Comparative Examples 1 to 3

An 1 L glass reactor equipped with a mechanical stirrer with turbineblades and a molecular oxygen gas inlet tube having a porous glass unitwas fed with β-isophorone, a manganese complex, a nitrogen-containingcompound, and the solvent in proportions shown in Table 1, and thereaction was carried out with an oxygen-containing gas (oxygenconcentration, volume %) flowing at a constant flow rate.

The conversions of β-isophorone and the selectivities of ketoisophoronefrom β-isophorone in Examples 1 to 8 and Comparative Examples 1 to 3 areshown in Table 1 with the reaction conditions.

TABLE 1 Nitrogen- Mn complex containing Amount of β-IP Amount of Mncomplex compound Amount of (concentration wt %) (mmol) Species AmountSolvent Example 1 133 g b-1 c-1  8.5 g 420 g (23.7) 0.24 g (0.41)Example 2 250 g b-1 c-1 10.0 g 320 g (43.1) 0.32 g (0.54) Example 3 250g b-1 c-2 12.2 g 320 g (42.9) 0.32 g (0.54) Example 4 200 g b-1 c-3 12.2g 370 g (34.4) 0.28 g (0.47) Example 5 300 g b-1 c-1 10.0 g 250 g (53.6)0.36 g (0.61) Example 6 200 g b-1 c-1 12.0 g 370 g (34.4) 0.28 g (0.47)Oxygen-containing gas Oxygen Reaction Flow rate concentrationTemperature Reaction Conversion Selectivity (L/min) (volume %) (° C.)Time (hr) (%) (%) Example 1 1.4 21 40 4 99 95 Example 2 1.8 21 40 4 9893 Example 3 1.8 21 40 4 98 90 Example 4 1.7 21 40 4 99 91 Example 5 2.021 45 4 98 88 Example 6 2.5 10 40 5 98 95

TABLE 2 Nitrogen- Mn complex containing Amount of β-IP Amount of Mncomplex compound Amount of (concentration wt %) (mmol) Species AmountSolvent Example 7 250 g b-1 c-4  9.5 g 320 g (43.1) 0.32 g (0.54)Example 8 133 g b-1 c-1  8.5 g 420 g (23.7) 0.32 g (0.41) Comp. Ex.1 200g b-2 c-5 18.0 g 410 g (31.8) 0.28 g (0.75) Comp. Ex.2 200 g b-2 c-112.0 g 370 g (34.4) 0.28 g 0.75 Comp. Ex.3 250 g b-2 c-5 26.0 g 290 g(44.2) 0.32 g (1.00) Oxygen-containing gas Oxygen Reaction Flow rateconcentration Temperature Reaction Conversion Selectivity (L/min)(volume %) (° C.) Time (hr) (%) (%) Example 7 1.5 21 35 6 99 92 Example8 1.2 21 40 5 99 93 Comp. Ex.1 1.4 21 40 4 21 80 Comp. Ex.2 1.5 21 40 487 90 Comp. Ex.3 1.0 100  40 4 85 71

As obvious from Tables 1 and 2. even if the concentration ofβ-isophorone is high and the oxygen concentration is low, the conversionand selectivity can be largely improved in Examples as compared withComparative Examples. Moreover, the conversion and selectivity can befurther improved by incorporating a nitrogen-containing compound.Further, even if the concentration of a manganese complex is small,ketoisophorone can be formed with high activities.

What is claimed is:
 1. An oxidation catalyst comprising a crystalline complex of manganese with an N,N′-disaliclidenediamine, wherein m+1 moles of the N,N′-disalicylidenediamine is coordinated to m moles of said manganese and m is a positive integer, and wherein the infrared spectrum of the complex indicates a hydroxyl group.
 2. An oxidation catalyst according to claim 1, wherein said N,N′-disalicylidenediamine is at least one member selected from the group consisting of N,N′-disalicylidene C₂₋₈ alkylenediamines and N,N′-disalicylidene C₆₋₁₂ arylenediamines.
 3. An oxidation catalyst according to claim 1, wherein said complex is shown by the following formula:

wherein R¹, R², and R³ are the same or different and each represents an alkylene group, a cycloalkylene group, or an arylene group and may have a substituent; R⁴ to R⁹ are the same or different and each represents hydrogen atom, a halogen atom, an alkyl group, a hydroxyl group, a hydroxymethyl group, or an alkoxy group; each of the rings Z is an aromatic ring; M stands for manganese; and n is 0 or an integer of not less than
 1. 4. An oxidation catalyst according to claim 1, wherein said complex is a complex of manganese having a valence of 2 to 4 with an N,N′-disalicylidene C₂₋₅ alkylenediamine.
 5. An oxidation catalyst according to claim 1, wherein the melting point of said complex is 190 to 240° C.
 6. An oxidation catalyst according to claim 1, wherein the melting point of said complex is 200 to 220° C.
 7. An oxidation catalyst comprising a complex recited in claim 1 and a basic nitrogen-containing compound.
 8. An oxidation catalyst according to claim 7, wherein said nitrogen-containing compound is an alicyclic or aromatic cyclic base having a plurality of nitrogen atoms.
 9. An oxidation catalyst according to claim 8, wherein the ring of said cyclic base contains at least one nitrogen atom.
 10. An oxidation catalyst according to claim 8, wherein said cyclic base has 2 to 6 nitrogen atoms.
 11. An oxidation catalyst according to claim 8, wherein said cyclic base is at least one member selected from the group consisting of 5- to 10-membered mono- and heterocyclic compounds, azabicyclo C₇₋₁₂ alkanes, azatricyclo C₈₋₁₆ alkanes, and aromatic heterocyclic compounds having (i) at least one nitrogen atom as a hetero atom, and (ii) an amino group or an N-substituted amino group or both.
 12. An oxidation catalyst according to claim 7, wherein said nitrogen-containing compound is a tertiary amine.
 13. An oxidation catalyst according to claim 7, wherein the proportion of said nitrogen-containing compound relative to said complex is 0.1/1 to 500/1 (molar ratio). 